Radar systems have heretofore been developed for measuring the speed of a target vehicle from a moving road patrol vehicle. In one type of system, two doppler signal components are developed, one being a reference signal component developed in response to reflections from the surface of a roadway or other stationary objects and the other being developed from reflections from a moving vehicle. By comparing the frequencies of the two doppler signal components, the speed of the moving target vehicle relative to the road surface can be determined. Such systems have been generally satisfactory in operation. However, there is a possibility that anomalies may be produced under certain conditions which, although unlikely to occur, have made it possible to challenge the absolute reliability or accuracy of indications obtained. For example, the reference signal component, which should be produced from reflections from the roadway to indicate the patrol car speed might be produced from other moving vehicles in the radar beam. There is also the possibility that false indications might be produced after double reflections from elements of a bridge or other structure.
In the prior art, little if any consideration has been given to possible alternatives which might avoid such objections and if consideration is given to possible alternatives, it will be found that they are such as to apparently operate in a manner such as to be even more objectionable. For example, if consideration is given to the development of a reference signal from the speed of rotation of the wheels of the patrol vehicle, it would appear that such a reference signal would be affected by the degree of inflation of the tires of the vehicle and might produce large inaccuracies.